Reductant delivery unit for automotive selective catalytic reduction with thermally optimized peak-and-hold actuation based on an injector open event

ABSTRACT

A trigger circuit is provided for a peak and hold driver circuit for a reductant delivery unit (RDU) having a solenoid-operated injector for selective catalytic reduction (SCR) after-treatment for vehicles. The peak and hold driver circuit is constructed and arranged to actuate the injector in a rise-to-peak current phase followed by a low current hold phase. The trigger circuit includes an injector open detection circuit constructed and arranged, based on a detected opening event of the injector, to trigger a transition from the rise-to-peak phase to the subsequent hold phase of the injector.

FIELD

The invention relates to a reductant delivery unit (RDU) that suppliesreducing agent to an engine exhaust system and, more particularly, to anRDU that improves on the overall electrical loading over a widetemperature range by triggering the transition from peak to hold basedon the detection of injector opening.

BACKGROUND

The advent of a new round of stringent emissions legislation in Europeand North America is driving the implementation of new exhaustafter-treatment systems, particularly for lean-burn technologies such ascompression-ignition (diesel) engines, and stratified-chargespark-ignited engines (usually with direct injection) that are operatingunder lean and ultra-lean conditions. Lean-burn engines exhibit highlevels of nitrogen oxide (NOx) emissions that are difficult to treat inoxygen-rich exhaust environments characteristic of lean-burn combustion.Exhaust after-treatment technologies are currently being developed thatwill treat NOx under these conditions. One of these technologiescomprises a catalyst that facilitates the reactions of ammonia (NH₃)with the exhaust nitrogen oxides (NOx) to produce nitrogen (N₂) andwater (H₂O). This technology is referred to as Selective CatalyticReduction (SCR).

Ammonia is difficult to handle in its pure form in the automotiveenvironment. Therefore, it is customary with these systems to use aliquid aqueous urea solution, typically at a 32% concentration of ureasolution (CO (NH₂)₂). The solution is referred to as AUS-32, and is alsoknown under its commercial name of AdBlue. The urea solution isdelivered to the hot exhaust stream and is transformed into ammonia inthe exhaust after undergoing thermolysis, or thermal decomposition, intoammonia and isocyanic acid (HNCO). The isocyanic acid then undergoes ahydrolysis with the water present in the exhaust and is transformed intoammonia and carbon dioxide (CO2). The ammonia resulting from thethermolysis and the hydrolysis then undergoes a catalyzed reaction withthe nitrogen oxides as described previously.

The AUS-32 injector is typically installed directly on the engineexhaust, which exposes it to a very hot environment. In order to reducethe electrical thermal loading of the injector, so-called peak-and-holdinjector drivers have been implemented. With reference to FIG. 1, thefunction of this driver is to actuate the injector in two modesdescribing the injector current: a rise-to-peak current phase, followedby a low current hold phase (current control at high switchingfrequency).

The low current level is typically at a value that is much lower thanthe full saturated current level of the injector, and higher than theminimum level of current needed to maintain the injector (solenoid)open. In today's driver circuits, the transition from the rise to peakto the hold phase is usually triggered by a current level detection onthe current; once the current reaches that level, the subsequent holdphase is enabled. FIG. 2 shows a peak-and-hold circuit 10 having aconventional peak current detection and trigger circuit 12.

The main advantage to operating the injector with a low hold phase isthe lower electrical load that results compared to operation undersaturated switch conditions. For example, an injector with a 12-ohmcoil, supplied by 14V, will dissipate 16.3 Watts (I=1.2 A). An injectorthat is operated with a 0.5 A hold mode will dissipate 7 Watts duringthe hold phase.

A disadvantage arises as the temperature increases and the injectorresistance increases. As the resistance increases, the time required forthe current to reach a given threshold will increase due to thedependence of the time on the coil resistance. In a limiting case with asufficiently high temperature, the current may never reach thetransition threshold, and yet the injector is open. The temperaturerange where this would occur is dependent on the difference between theselected transition current level and the minimum current required toopen the injector. This difference will be non-zero to take into accounttolerances and variations of the various elements that make up theelectrical and magnetic circuits.

As an example, today the peak current is specified at a level of 0.8 A.This is above the required nominal opening current of 0.6 A. Thespecified nominal hold current is 0.5 A. A situation could arise wherethe saturated injector current is 0.7 A, for example, if the availableelectrical supply voltage is only 12V, but the injector coil resistanceis 17Ω, (e.g., the injector coil temperature is 130 C). An illustrationof what the current waveform would look like in this case is shown inFIG. 3. The risk of this condition is then to have an injector operatingalready at an elevated temperature that is subjected to an increasedelectrical thermal load.

Thus, there is a need for an RDU that improves on the overall electricalloading over a wide temperature range by triggering the transition frompeak to hold based on the detection of injector opening.

SUMMARY

An object of the invention is to fulfill the needs referred to above. Inaccordance with the principles of the present invention, this objectiveis obtained by a trigger circuit for a peak and hold driver circuit fora reductant delivery unit (RDU) having a solenoid-operated injector forselective catalytic reduction (SCR) after-treatment for vehicles. Thepeak and hold driver circuit is constructed and arranged to actuate theinjector in a rise-to-peak current phase followed by a low current holdphase. The trigger circuit includes an injector open detection circuitconstructed and arranged, based on a detected opening event of theinjector, to trigger a transition from the rise-to-peak phase to thesubsequent hold phase of the injector.

In accordance with another aspect of an embodiment, a reductant deliveryunit (RDU) and control unit for selective catalytic reduction (SCR)after-treatment for vehicles includes an RDU having a solenoid-operatedinjector. A control unit is electrically connected with the solenoid.The control unit has a peak and hold driver circuit constructed andarranged to actuate the injector in a rise-to-peak current phasefollowed by a low current hold phase. The driver circuit includes aninjector open detection circuit constructed and arranged, based on adetected opening event of the injector, to trigger a transition from therise-to-peak phase to the subsequent hold phase of the injector.

In accordance with yet another aspect of an embodiment, a method oftriggering a reductant delivery unit (RDU) having a solenoid-operatedinjector for selective catalytic reduction (SCR) after-treatment forvehicles detects an opening event of the injector, and based on thedetecting, step, triggers a transition from a rise-to-peak phase to asubsequent hold phase of the injector, thereby limiting a thermal loadon the injector to a minimum required to ensure opening of the injector.

Other objects, features and characteristics of the present invention, aswell as the methods of operation and the functions of the relatedelements of the structure, the combination of parts and economics ofmanufacture will become more apparent upon consideration of thefollowing detailed description and appended claims with reference to theaccompanying drawings, all of which form a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from the following detaileddescription of the preferred embodiments thereof, taken in conjunctionwith the accompanying drawings, wherein like reference numerals refer tolike parts, in which:

FIG. 1 is view of conventional injector current, showing rise-to-peakphase followed by a low current hold phase.

FIG. 2 is a block diagram of a conventional peak-and-hold circuit with apeak current detection and trigger circuit.

FIG. 3 is view of a conventional current waveform showing saturationcurrent at 0.7 A.

FIG. 4 shows conventional opening event detection of an injector bycurrent analysis.

FIG. 5 shows detection of opening time from second derivative of coilcurrent.

FIG. 6 is a peak-and-hold circuit block diagram with an injector opendetection circuit provided in accordance with an embodiment.

FIG. 7 shows a current waveform that results from the circuit of FIG. 6.

FIG. 8 is a view of a control unit containing the circuits of FIG. 6 foroperating an RDU.

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

The disclosed embodiment relates to a control strategy to eliminate therisk of an undesirable increase in the thermal load of an injector of anRDU at already elevated operating temperatures. The detection ofinjector opening and closing events by analysis of the voltage orcurrent is well known. An example of an opening event detection bycurrent analysis (indicated by “OPP2”) is shown in FIG. 4, where theaccelerometer signal is 14, the voltage signal is 16, the test pulse is18, and the current signal is 20.

The detection of these events is useful for diagnostics purposes, andcan also be used to compensate for lifetime shifts in flow due tochanges in the duration of the injector transient phase. With referenceto FIG. 5, one embodiment of such detection is in hardware form with acircuit that generates an electrical pulse 22 upon the opening detectionusing the second derivative 24 of the current waveform as an input. Thespurious initial pulse 26 can be ignored by appropriate use of enablewindows, e.g., only allowing the pulse through during certainpre-determined times during the injector pulse-width. An example ofusing the second derivative of current in detecting a state of aninjector is disclosed in co-pending, U.S. Provisional Application, filedon the same date as this regular application, entitled,“Solenoid-Actuator-Armature End-of-Motion Detection, Attorney DocketNumber: 2012P02238US, the contents of which is hereby incorporated byreference into this specification.

With reference to FIG. 6, a block diagram is shown of a peak-and-holddriver circuit 10′ constructed and arranged to actuate an injector in arise-to-peak current phase followed by a low current hold phase inaccordance with an embodiment. The circuit 10′ includes a triggercircuit 28 having an injector open detection circuit 29. Thus, thetrigger circuit 28 replaces the prior art current threshold triggercircuit 12 of FIG. 2. The circuit 10′ uses the injector opening event,as detected, for example, by use of the second derivative 24 of thecurrent waveform noted above, to trigger the transition from therise-to-peak phase to the subsequent hold phase of the injectoractuation control. In the embodiment, the detection circuit 29 includesa processing or differentiating circuit 31 for differentiating current.Other conventional methods of detecting an opening state of an actuatoror injector can be used instead of using the second derivative ofcurrent. An illustration of the current waveform 30 that would resultfrom implementation of the embodiment is shown in FIG. 7.

With reference to FIG. 8, the circuit 10′ including the trigger circuit28 is preferably provided in a control unit 32 that is electricallyconnected to a solenoid operated injector 34 of an RDU, generallyindicated at 36. The RDU 36 can be employed in a system of the typedisclosed in U.S. Patent Application Publication No. 2008/0236147 A1,the contents of which is hereby incorporated by reference into thisspecification.

The RDU 36 includes the solenoid fluid injector 34 that provides ametering function of fluid and provides the spray preparation of thefluid into the exhaust gas flow path of a vehicle in a dosingapplication. The fluid injector 34 is preferably a gasoline,electrically operated, solenoid (coil) fuel injector such as the typedisclosed in U.S. Pat. No. 6,685,112, the content of which is herebyincorporated by reference into this specification. Thus, when the coilof the injector 34 is energized, a valve in the injector opens, causingreductant to be delivered to an exhaust flow path in the conventionalmanner.

By using the injector opening event as a trigger, the thermal loading ofthe injector is thereby limited to the minimum required to ensureopening of the injector. The risk of a drawn-out rise-to-peak phase andtherefore additional thermal loading is also avoided.

The foregoing preferred embodiments have been shown and described forthe purposes of illustrating the structural and functional principles ofthe present invention, as well as illustrating the methods of employingthe preferred embodiments and are subject to change without departingfrom such principles. Therefore, this invention includes allmodifications encompassed within the spirit of the following claims.

What is claimed is:
 1. A trigger circuit for a peak and hold drivercircuit for a reductant delivery unit (RDU) having a solenoid-operatedinjector for selective catalytic reduction (SCR) after-treatment forvehicles, the peak and hold driver circuit being constructed andarranged to actuate the injector in a rise-to-peak current phasefollowed by a low current hold phase, the trigger circuit comprising: aninjector open detection circuit constructed and arranged, based on adetected opening event of the injector, to trigger a transition from therise-to-peak phase to the subsequent hold phase of the injector.
 2. Thetrigger circuit of claim 1, in combination with the driver circuit sothat the driver circuit includes the trigger circuit.
 3. The combinationof claim 2, in further combination with the RDU.
 4. The combination ofclaim 3, wherein the driver circuit and trigger circuit are part of acontrol unit electrically connected with the RDU.
 5. The trigger circuitof claim 1, wherein the open detection circuit is constructed andarranged to trigger the transition based on an electrical pulsegenerated upon detecting the opening event of the injector by using asecond derivative of a current waveform as an input.
 6. The triggercircuit of claim 5, wherein the open detection circuit includes adifferentiating circuit.
 7. A reductant delivery unit (RDU) and controlunit for selective catalytic reduction (SCR) after-treatment forvehicles, the RDU and control unit comprising: an RDU having asolenoid-operated injector, and a control unit electrically connectedwith the injector, the control unit having a peak and hold drivercircuit constructed and arranged to actuate the injector in arise-to-peak current phase followed by a low current hold phase, thedriver circuit including an injector open detection circuit constructedand arranged, based on a detected opening event of the injector, totrigger a transition from the rise-to-peak phase to the subsequent holdphase of the injector.
 8. The RDU and control unit of claim 7, whereinthe injector open detection circuit is constructed and arranged totrigger the transition based on an electrical pulse generated upondetecting the opening event of the injector by using a second derivativeof a current waveform as an input
 9. The RDU and control unit of claim8, wherein the injector open detection circuit includes adifferentiating circuit.
 10. A method of triggering a reductant deliveryunit (RDU) having a solenoid-operated injector for selective catalyticreduction (SCR) after-treatment for vehicles, the method comprising:detecting an opening event of the injector, and based on the detecting,step, triggering a transition from a rise-to-peak phase to a subsequenthold phase of the injector, thereby limiting a thermal load on theinjector to a minimum required to ensure opening of the injector. 11.The method of claim 10, wherein the detecting step uses a secondderivative of a current waveform of the injector.